1. Field of the Invention:
The present invention relates to an automobile air conditioner including a heat pump for heating and cooling the vehicle passenger compartment.
2. Description of the Prior Art:
Heaters generally used in automobiles are so-called "hot water heaters" in which engine cooling water (hot water) is utilized as a heat-transfer medium. When the engine starts up in winter, it takes long time to heat the engine cooling water at a sufficient temperature and hence an immediate heating of the vehicle passenger compartment is difficult to obtain.
With the foregoing drawback in view, an attempt has been proposed in which the hot water heater is replaced by a heat pump air-conditioner employing the outside air as a heat source. In the proposed heat pump air-conditioner such as disclosed, for example, in Japanese Patent Laid-open Publication No. 52-25341, the cooling system of an automobile air-conditioner is switched to a heat pump system wherein heat taken up from the outside air through a heat exchanger disposed outside the vehicle passenger compartment is recovered through another heat exchanger disposed inside the vehicle passenger compartment.
Inasmuch as the outside air is employed as a heat source, only an insufficient amount of heat can be taken up through the exterior heat exchanger when the outside air temperature is low. Accordingly, a sufficient heating effect is not provided by the disclosed heat pump air conditioner.
According to a modified heat pump air-conditioner disclosed in Japanese Patent Publication No. 60-236821, there is provided a third heat exchanger for taking up or absorbing heat from an engine cooling water during the heating operation mode.
The engine cooling water requires a long time for warming up and hence is regarded as an effective heat source for the heat pump air-conditioner capable of producing a quick heating effect. Regardless of the provision of the third heat exchanger, only two of three heat exchangers are engaged in the operation when the air-conditioner is operating in the heating mode or the cooling mode. As a result that, a certain amount of refrigerant is left unused in one heat exchanger which is not engaged in the heating or cooling operation. Due to such marooned inoperative refrigerant whose amount varies with atmospheric conditions and running conditions of the preceding operation, the amount of operative refrigerant in the cooling cycle becomes instable. In case of a large amount of refrigerant, the pressure becomes high. When the refrigerant is short, then an insufficient heating and cooling effect is produced.
According to another prior proposal disclosed in Japanese Utility Model Laid-open Publication No. 51-69455, a hot air outlet is disposed in front of the exterior heat exchanger for discharging hot air which is obtained through heat exchange operation with respect to engine exhaust gas so as to provide a heat source of a large capacity.
The disclosed arrangement requires a duct and an exhaust gas heat exchanger in addition to the hot air outlet stated above. Furthermore, the hot air outlet is disposed in face to face confrontation to an exterior heat exchanger disposed on the front face of an automobile so that part of heat is wasted to the outside air before it is transferred to the exterior heat exchanger. Thus, the overall thermal efficiency of the air-conditioner is considerably reduced.